Method for measuring and controlling fiber variations in paper sheet

ABSTRACT

A formation control method and apparatus in which an image is emitted from a light source and transmitted through a predetermined area of paper an captured by a camera to be displayed as transmitted light image on a display of an image processing computing element, the transmitted light image displayed on the display being image-analyzed to obtain formation factor for quantification of the formation, J/W ratio and the like being optimized by fuzzy control using membership functions based on said formation factor so as to improve the formation.

This application is a continuation-in-part of application Ser. No.07/640,409, filed Jan. 23, 1991, now abandoned.

TECHNICAL FIELD

The present invention relates to a formation measuring method toidentify unevenness of transmitted light on paper as a plane image andto evaluate the property and the quality of the paper so as to controlquality improvement and also relates to a formation control method andapparatus using said formation measuring method.

BACKGROUND ART

Quality of paper formation (minute uneven thickness) indicates thedegree of fiber variance in paper sheet. The measurement of the degreeof fiber variance takes into account the size and distribution of holes,flock distribution, and dust particle measurement. Generally, this hasbeen checked by placing a sample sheet on an inspection boxaccommodating a light source to visually examine transparencydistribution of the sheet.

This method, which is widely used in factories, is rather of subjectivenature and results of the inspection varies according to each inspectorsince sufficient knowledge and long experience are required for suchinspection.

For this reason, a formation meter as shown in FIG. 1 has been developedand is practically used. This formation meter comprises upper and lowerheads b and c above and below the running paper a to be measured, thelower head c accommodating a light source d such as laser connected toan electric power source and a mirror f for irradiating the light fromsaid light source d onto the paper a. The upper head b accommodates aphotocell j for receiving the light e, which has passed through saidpaper a via a mirror g, a filter h and a lens i.

The light e from the light source d is irradiated on the paper a throughthe mirror f; the light e passing through the paper a enters thephotocell j through a mirror g, a filter h and a lens i and is convertedto voltage and is outputted. As shown in FIG. 2, the voltage value isindicated as formation index relative to the time.

When the formation index is measured, jet/wire ratio (J/W ratio) and thelike are changed according to said formation index by judgment of aninspector to obtain better formation.

DISCLOSURE OF INVENTION

In the above-mentioned formation meter, however, the diameter of thelight e irradiated from the light source d to the paper a is about 1 mmand any fluctuation of transmitted light level is detected as flock sizethrough one-dimensional processing of the transmitted light signal.Although the formation of the paper a is converted to numerical value,the sample for judgment is too small to make total judgment for accurateidentification of the formation as judgment through human vision.

In the control of the formation, J/W ratio is adjusted only by trial anderror. Because of the control being based on measurement results by theabove-mentioned formation meter, which does not necessarily reflect thetotal conditions, improvement of the paper quality is rather difficult.

The present invention was made to overcome such disadvantages of theprior art and will provide a formation measuring method for moreaccurate evaluation of the formation objectively not as point but asplane. The present invention will further provide a formationcontrolling method and apparatus for efficient improvement of paperquality according to results of measurement by the formation measuringmethod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of conventional formation meters;

FIG. 2 is a diagram showing the relationship between time and formationindex as obtained by the formation meter in FIG. 1;

FIG. 3 shows an embodiment of an apparatus for carrying out theformation measuring method of the present invention as well as theformation controlling method using said formation measuring method;

FIGS. 4(a), 4(b), 4(c), 4(d) and 4(d') are views to explain the imageprocessing on a display unit;

FIG. 5 is a schematic illustration of the relationship between windowsand pixels on the display unit;

FIG. 6 is a view to explain the image in the case where frequencyanalysis is performed on the pixels which constitute the image;

FIG. 7 is a diagram showing results of frequency analysis;

FIG. 8 is to explain a variation of image processing on image display inthe formation measuring method of the present invention;

FIG. 9 is a general side view showing sites of installation of formationmeters each comprising stroboscope and camera;

FIG. 10 is a variation curve diagram showing the relationship betweencamera aperture and formation factor;

FIG. 11 is a diagram showing a membership function obtained on one ofthe formation factors;

FIG. 12 is a diagram showing how to obtain the center of gravity bysynthesizing the membership functions to the variation curves of aplurality of formation factors;

FIG. 13 is a side view of wire part of a paper machine;

FIGS. 14(i), 14(ii), 14(iii), 14(iv), 14(v) and 14(vi) are to explainthe procedure to determine the change of J/W ratio according to theformation factors;

FIG. 15 is a flow chart of an example of the formation controllingmethod using the formation measuring method of the present invention;

FIG. 16 shows an arrangement of another embodiment comprising aplurality of cameras with different visual fields;

FIG. 17 is a lateral sectional view of a formation meter which grasps orcatches images in wide and narrow visual fields;

FIGS. 18(a) and 18(b) are variation curve diagrams showing therelationship between J/W ratio and formation factor A;

FIGS. 19(a) and 19(b) are membership function diagrams showing therelationship between J/W ratio and evaluation values for formationfactor A;

FIG. 20 is a wide-narrow visual field membership function diagramobtained by overlapping FIGS. 19(a) and 19(b);

FIGS. 21(a) and 21(b) are variation curve diagrams showing therelationship between J/W ratio and formation factor B;

FIGS. 22(a) and 22(b) are membership function diagrams showing therelationship between J/W ratio and evaluation values for formationfactor B;

FIG. 23 is a wide-narrow visual field membership function diagramobtained by overlapping FIGS. 22(a) and 22(b);

FIG. 24 is a general membership function diagram obtained by overlappingFIGS. 20 and 23; and

FIG. 25 is a flow chart showing the flow of coarse and fine controls.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, embodiments of the present invention will be describedin connection with the drawings.

FIGS. 3, 4 and 5 show an embodiment of the present invention in whichdisposed on one side of the paper 1 to be measured is a light source box2a accommodating a light source 2 such as source of parallel beamshaving variable light quantity. Arranged on its opposite side is acamera box 3a which is movable in widthwise and vertical directions ofthe paper 1 relative to the rail 3c. The camera box 3a accommodates acamera 3 having zooming function and with an automatic aperture controldevice 3b to make up a formation meter 50. A CCD (charge coupled device)frame accumulation mode camera or its equivalent is used as camera 3 ofthis embodiment in combination with a stroboscope 2. The camera 3 isconnected through a cable 4 with a computing element 5 for imageprocessing having a display unit 6. The camera 3 is further connectedwith another display unit 7 through a cable 8 so as to permanentlydisplay transmitted light image of the paper 1. The computing element 5for image processing is connected with the automatic aperture controldevice 3b through a cable 40 so that a control signal from the imageprocessing computing element 5 is inputted to the automatic aperturecontrol device 3b to perform automatic control of the aperture.

To the image processing computing element 5, a fuzzy control device 110comprising a control computer 100 and a controller 101 for control isarranged for the controlling purpose. The image processing computerelement 5 is connected with the control computer 100 through a formationsignal line 102 and a control signal line 103. The computer 100 isconnected with the controller 101 through communication lines 104.Further, connected with the controller 101 through the control signallines 105 are an actuator for changing a ratio of the speed of jetinjected from a below-mentioned head box 10 in FIG. 13 to the wirespeeds of bottom and top wires 12 and 16, an actuator for changing theangle of foils 14 and the like.

Since the paper 1 to be inspected is of considerable size, a portion ofthe paper to be picked up by the camera 3 as sample (10 mm×10 mm ormore) is to represent all features of the paper 1 and include anapparent steady area or area where quality of the entire paper 1 can bejudged by inspecting this area.

During measurement, adjustment is made such that an adequate quantity oftransmitted light is obtained from the light source 2 according to thethickness of the paper 1. As to adjustment of aperture of the camera 3,description will be given later. A signal representative an imageentering the camera 3 enters the display unit 7 and forms an image 9a oftransmitted light on the paper 1. On the other hand, the image signalentering the image processing computing element 5 is displayed on thedisplay unit 6 as an image 9 in FIG. 4(a) showing an area by which thequality of the entire paper 1 is determinable. On the screen, theconcentration of holes and the like is displayed thinner (lighter) thanaverage and overweighted portions with dust and the like attachedthereto are displayed denser (darker) than the average.

On the image 9, a predetermined number of windows W₁, W₂, . . . , W_(k),. . . , W_(N) are set which have an area by about two times as large asthe average size of hole or the minimum size of flock peculiar to paperas a variance calculation unit (FIG. 4(b)). The size and number of thewindows can be selected according to the grade, furnish or the like ofpaper.

Pixels of the display unit 6 may be contained by the quantity of M=n×m(n=4 and m=5 in the example shown) in a window in FIG. 5. The tonedensity (referred to hereinafter simply as density) of the pixels inline i and row j in the k-th window W_(k) is expressed by C_(kij). Thus,the average value of density C_(aVk) in k-th window W_(k) can becalculated as: ##EQU1## The variance V_(aVk) of the density in k-thwindow W_(k) (hereinafter referred as primary variance), i.e. thevariation of density in a window W_(k) is calculated as (See FIG. 4(c)):##EQU2##

Further, the average value a_(V) of primary variance for all windows W₁,W₂, . . . , W_(k), . . . , W_(N) is calculated: ##EQU3## Based on theaverage value a_(V) of primary variance of all windows, the varianceV_(aV) of primary variance for all windows W₁, W₂, . . . , W_(k), . . ., W_(N) (hereinafter referred as secondary variance) is calculated:##EQU4## And the results of the calculation are displayed (See FIG. 4(d)).

The average value a_(V) of primary variance for all windows expressesthe macro variance on the screen. The formation can be quantitativelydetermined as the formation factor in relatively wide visual field(formation factor in the case where paper is not even, e.g. the paperhaving serious defect). In the evaluation in the final stage of controlwhere the entire paper is uniform and formation is evaluated bymicrojudgment, the formation can be quantitatively determined using thevariance V_(aV) (secondary variance) of primary variance of density forall windows as the formation factor.

Further, in addition to the average value a_(V) of primary variance forall windows and to the secondary variance V_(aV) for all windows as awhole, the variance of average value C_(aVk) in the windows W₁, W₂, . .. , W_(k), . . . , W_(N) is calculated: ##EQU5## and the results ofcalculation may be displayed (See FIG. 4 (d')). The variance V_(aaV) ofaverage value of the density for each window expresses variance V_(aaV)of average value of the density for each window expresses macro-varianceof light and dark to average density on the screen and can be used asformation factor for quantitative determination of the formation when itis uniform as a whole and density is very uneven.

It is needless to say that in this case formation may be quantitativelydetermined using a formation factor through combination of a_(V),V_(aaV) and V_(aV) according to object.

Connected to the image processing computing element 5 are a datum logger(not shown) for accumulating density datum for pixels of columns a₁ -a_(n) in b_(i) -th row or rows b₁ - b_(n) in a_(i) -th column composingthe image 9 displayed on the display unit 6 as shown in FIG. 6 as wellas an analyzer (not shown) for pulling out datum from the data logger tograsp them as changes over time for frequency analysis. Alternatively,the data accumulated in the data logger is processed by analysissoftware. Thus, judgment may be made whether the pulsating component ispresent or not in the paper 1 according to results of frequency analysisin longitudinal direction (along length of the paper 1). Frequencyanalysis in lateral direction (along width of the paper 1) may be madeusing stroboscope as the light source 2 unlike conventional way oftransmitted light being caught by spot, so that features correspondingto the flock can be expressed, reproducing the density of formation withhigh fidelity. Accordingly, whether the formation is pulling formationor pushing formation can be easily judged. Pulling formation is thestatus where flock is extended in form of lines while pushing formationis the status where flock is in form of scales. In FIG. 7 with averagedensity taken on ordinate and frequency on abscissa, the ideal formationis shown by two-dot chain line while pulling formation is given by solidline and pushing formation by broken line respectively.

FIGS. 8(a)-8(e) show the variations in display of the image in theformation measuring method of the present invention. For moreclarification of the image 9 displayed on the display unit 6,three-value image processing is performed, expressing the density bythree steps of `dense`, `moderate` and `light` to display the image 9'as shown in FIG. 8(b). The ratio of the sum ΣS_(V) of areas 30 withmaximum transmitted light on said image 9' to the total area S, i.e.void ratio V.sub.θ is calculated as: ##EQU6## The ratio of the sumΣS_(K) of areas 31 with minimum transmitted light on said image 9' tothe total area S, i.e. overweight ratio K is calculated as: ##EQU7## anddisplayed (FIG. 8 (c)). Thus, the formation of the paper 1 isquantitatively determined. If necessary, apparent defects in said image9 or apparently satisfactory portions of the image 9 are displayed asenlarged image 9" as shown in FIG. 8(d) which is image-processed withexpression of the density in three steps so that enlarged image 9"' ofFIG. 8(e) is displayed, which in turns is used as material foridentification of the cause of the formation.

In the example shown in FIGS. 8(a)-8(e), plane information can beobtained by image processing with features of the paper 1 emphasized.Above all, holes, dust and the like which are not assessable in the pastcan be detected in earlier stage, thus contributing to improvement ofquality and enhancement of productivity. Also, most satisfactory part ormost unsatisfactory part of the image can be picked up and easilyanalyzed.

The formation meter comprising the light source 2 and the camera 3 usedin the formation measuring method as described above may be installed inany cite such as wire part, press part, dryer part, calender part andlike in FIG. 9.

Now, to determine the aperture of the camera 3 will be described.

One of the formation factors obtained above such as the average valuea_(V) of primary variance of density, secondary variance V_(aV) ofdensity, variance V_(aaV) of average value of density, analyticalspecification of frequency in lateral direction and hole specificationis named A, other as B, and still other as C, . . . . Values offormation factors A, B, C, . . . are obtained with the aperture of thecamera 3 being changed at constant interval as shown in FIG. 10. Resultsare variation curves having maximum or minimum values (maximum shown inthe figure). Each maximum point a₁, b₁, c₁, . . . of the curves mosttypically represents the features of the formation factors A, B, C, . .. , respectively.

Through the data processing of each of the variation curves of theformation factors A, B, C, . . . , membership functions in triangular orrod-like form as shown in FIG. 11 (only the membership function A'related to formation factor A is given in the figure) is obtained withevaluation value of maximum being 1. By synthesizing each of themembership functions A', B', C', . . . thus obtained, a center ofgravity X (center of gravity of the area) is obtained as given in FIG.12.

This point X is the aperture of the camera 3.

The aperture of the camera 3 is automatically adjusted by the controlsignal from the image processing computing element 5 to the automaticaperture device 3b so that the aperture will be equal to the value thusobtained.

By the above procedure, the aperture of the camera 3 can beautomatically selected so that the most characteristic information ofthe sample can be obtained. Accordingly, formation can be measured moreaccurately, causing no individual difference in measurement results.

Thus, it is possible to quantitatively determine the formation as plane,not as points like the prior art, and to evaluate formation moreaccurately and objectively, and further to utilize the formation factorsfor the control of J/W ratio, drainage and the like.

Use of stroboscope as the light source 2 will make it possible to applythe formation measuring method as described above not only to off-lineoperation but also to on-line operation with high speed (1500 m/min. orso) and high basis weight (basis weight: about 300 g/m²).

Advantages in the use of stroboscope as light source 2 are as follows:

(1) There is less deviation of screen during high-speed on-linemeasurement and no trouble occurs on the analysis of pixels on thescreen due to the deviation on screen.

(2) When shuttering the camera, density can be expressed in three stepsof `dense`, `moderate` and `light` to clearly define the image up to theanalysis of three-value imaging; but it is not suitable for detectingslight density such as formation meter. Combination of stroboscope withnon-shuttering camera is more suitable for high-speed photographing todetect the density.

(3) Because high light quantity can be easily obtained by stroboscope(pulse light source), (a) the aperture of camera can be reduced duringphotographing, which minimizes the influence of disturbance, and (b)even thicker paper can easily transmit light.

(4) There is speed limit in using mechanical shuttering whereas,needless to say, combination of stroboscope with electrical shutteringenables photographing of image at higher speed.

Advantages of CCD frame accumulated mode camera are that still image canbe photographed by stroboscope and the image signal can be equallyincorporated.

Next, description is given on the method for controlling formationthrough application of the concept of membership function based on theformation factors obtained by the above formation measuring method (SeeR. Yamakawa: `Concept of Fuzzy Computer`; Nov. 10, 1988, 3rd print;Kodansha).

The control is performed through fuzzy control unit 110 comprising thecontrol computer 100 and the controller 101 in FIG. 3 based on theformation factors obtained by the image processing computing element 5.

FIG. 13 is a side view showing the wire part of a paper machine, where10 represents a head box; 11, a breast roll; 12, bottom wire; 13, aforming board; 14, foils; 15, a wet suction box; 16, top wire; 17 and18, deflectors; 19, a suction box; 20 and 21, showers to wash off dustattached on bottom wire 12 and top wire 16; 22 and 23, automatic valvesfor adjusting quantity of water from the showers 20 and 21; and 24,felt. The foils 14 are drainage elements of the initial drainage area25. The angle of the foils 14 with respect to the bottom wire 12 may beadjusted to alter the pressure applied by suction from the drainagearea. Deflectors 17,18 form part of the secondary drainage area 26, 27.There is an overlap along the bottom wire 12 between the top edge of thebottom deflector 17 and the bottom edge of the top deflector 18. Therelative clearance between the top and bottom edges is known as thedeflector pushing degree. The deflector pushing degree and angles of thedeflectors are both adjustable to affect the secondary drainageparameters. J/W ratio (the ratio of jet speed injected from the head box10 to the speed of bottom and top wires 12 and 16), angles of the foils14 at an initial drainage area 25, pushing degrees of the deflectors 17and 18 at a bottom secondary drainage area 26 and at a top secondarydrainage area 27 are changed respectively according to the formationfactors obtained by the above formation measuring method. Suctionquantity of the suction box 19 and openings of the automatic valves 22and 23 of the showers 20 and 21 are changed if necessary.

The method of the invention wherein generated membership curves are usedin conjunction with operation factors of a paper making apparatus tooptimize to paper quality will now be explained with reference to FIG.14, as set forth in steps (1) through (4) below. Based on experimentaldata performed in advance, membership function curves are obtained inadvance as shown in FIGS. 14(i)-14(v): (1) five membership functionscurves for formation M₁ -M₅ to specify the quality of the paper 1 infive steps of `worst`, `bad`, `normal`, `good` and `best` from thedegree (ordinate) corresponding to formation factor (abscissa) of thepaper 1 and (2) five membership function curves for control M_(1a)-M_(5a) and M_(1b) -M_(5b) to the corresponding degree (ordinate) to thechanges (abscissa) of J/W ratio (only increase or decrease of wire speedin this case) in response to each of the membership function curves M₁-M₅ to specify the quality of the paper 1.

(3) Degree of matching at intersections of the formation factors of thepaper 1 obtained by the formation measuring method with each of themembership function curves M₁ -M₅ to specify the quality of the paper 1is obtained. (4) In correspondence to each of the matching degrees,results of the estimated J/W ratio changes are obtained from therespective membership function curves M_(1a) -M_(5a) and M_(1b) -M_(5b)showing changes of the J/W ratio. Further, results of the estimatedchange of J/W ratio are overlapped and synthesized and final membershipfunctions M_(La) and M_(Lb) showing final estimated results of the J/Wratio change are found as shown in FIG. 14(vi). Abscissa component ofeither of the gravity centers of the final membership functions M_(La)and M_(Lb) where the area surrounded by final membership function M_(La)ordinate or M_(Lb) ordinate and abscissa is halved is used as incrementor decrement of the actual wire speed, determining actual change of J/Wratio for control of J/W ratio.

FIG. 14 shows a case where the formation factor is 35. Since ordinatecomponent (matching degree) of the intersection with the membershipfunction curve M₁ showing `worst` of FIG. 14(i) is about 0.25, the headof the control membership function curve M_(1a) or M_(1b) to`extensively increase` or `extensively decrease` wire speed by extendingthe line horizontally from the intersection is scraped off at about 0.25of the matching degree and only hatched portion is adopted as estimatedresult of increment or decrement of the wire speed. Also, since ordinatecomponent (matching degree) of the intersection with the membershipfunction curve M₂ showing `bad` of FIG. 14(ii) is about 0.75, the linefrom the intersection is extended, the head of the control membershipfunction curve M_(2a) or M_(2b) to `increase` or `decrease` wire speedis scraped off at about 0.75 of matching degree and only hatched portionis adopted as estimated result of increment or decrement of the wirespeed. Further, since ordinate component (matching degree) of theintersection with the membership function M₃ showing `normal` of FIG.14(iii) is about 0.7, the line from the intersection is extendedhorizontally, the head of control membership function curve M_(3a) orM_(3b) to `fairly increase` or `fairly decrease` the wire speed isscraped off at about 0.7 of the matching degree and only hatched portionis adopted as estimated results of increment or the decrement of wirespeed. Also, since ordinate component (matching degree) of theintersection with the membership function curve M₄ showing `good` ofFIG. 14(iv) is about 0.1, the line from the intersection is extendedhorizontally, the head of the control membership function curve M_(4a)or M_(4b) to `slightly increase` or `slightly decrease` the wire speedis scraped off at about 0.1 of the matching degree and only hatchedportion is adopted as estimated result of increment or decrement of thewire speed. Further, with the formation factor being 35 in relation tothe membership function curve M₅ showing `best` of FIG. 14(v), there isno intersection. Therefore, the matching degree to the controlmembership function curve M_(5a) or M_(5b) to `not increase` or `notdecrease` the wire speed is 0, i.e. it is necessary to increase ordecrease the wire speed. Accordingly, with the formation factor being 35or so, overlap and synthesis of the estimated results lead to the centerof gravity being located between `fairly increase` and `increase` orbetween `fairly decrease` and `decrease` where matching degree isrelatively high as shown in FIG. 14(vi) and increment or decrement ofwire speed is determined. For the judgment on whether to increase or todecrease the wire speed, one of the centers of gravity (e.g. the centerof gravity to decrease) is adopted from the final estimated result. Inthe case where improvement of formation is noted (i.e. the differencebetween the formation factor before the control and the formation factorduring the control is positive), control is performed to decrease thewire speed. In the case where improvement of formation is not noted(i.e. the difference between formation factor before the control and theformation factor during control is negative), control is performedthereafter in the direction to increase the wire speed. Thus, moreefficient control can be achieved.

In this way, by adopting the fuzzy theory using membership functions, itis possible to perform not on-off control but mild control withoutgiving radical change on the paper 1.

When J/W ratio is changed in this way and no further improvement offormation is found by the repeated change of J/W ratio as shown in FIG.15, the formation is improved by a fine tuning method by controlling insequence the foil angle until no further improvement is noted, and thenthe deflector pushing degree until no further improvement is noted.

In controlling the J/W ratio, it is possible to increase J/W ratio inthe case of pulling formation and to decrease J/W ratio in the case ofpushing formation, using the results of frequency analysis (i.e. whetherthe formation is pulling or pushing) of the density of the image inlateral direction. In so doing, formation control can be achievedreliably and efficiently.

Further, it is possible to observe the entire formation by lifting thecamera 3 along the rail 3c in FIG. 3 to widen visual field of the camera3 at the starting of measurement. The visual field of the camera 2 isgradually narrowed down by moving down the camera 3 along the rail 3c asthe formation is improved by the formation control method after startingthe control. When the formation is substantially stabilized and thecontrol is almost completed, the camera 3 may be lifted up again alongthe rail 3c to return to the initial large visual field for monitoring.

This contributes to the fine control of the formation and is useful tocope with changes of external conditions such as change of raw materialcondition after the formation is stabilized.

FIG. 16 shows another embodiment of the changed visual field in whichautomatic aperture devices 3b-1 and 3b-2 are incorporated. A pluralityof (two in the figure shown) cameras 3-1 and 3-2 accommodated in cameraboxes 3a-1 and 3a-2 are arranged on one side of the paper 1, and thelight sources 2-1 and 2-2 accommodated in light source boxes 2a-1 and2a-2 are arranged on the other side to make up a formation meter 50'. Itis preferable to dispose the cameras 3-1 and 3-2 in the feedingdirection of the paper 1.

Before starting and after completion of the control, the image is caughtby the camera 3-2 with wider visual field and its signal is sent throughthe cable 8-2 to the display unit 7 and through the cable 4-2 to theimage processing computing element 5. When the formation is improvedafter the starting of control and requirements for judging fine variancecan be met, changeover to the camera 3-1 with narrower visual field iseffected. Its signal is sent to the display unit 7 through the cable 8-1and to the image processing computing element 5 through the cable 4-1for further processing.

Although a plurality of cameras are required for such procedure, thecameras need not to be moved for change of visual field and may befixed. The visual field can be quickly changed simply by switching overthe plural cameras.

FIG. 17 shows a formation meter 50" in which images in wide and narrowvisual fields are concurrently caught by a plurality of cameras withdifferent visual fields and each of these images are introduced to theimage processing computing element 5 (FIG. 3). In this formation member50", support stands 71-1 and 71-2 are installed vertically movably alongthe rails 3c-1 and 3c-2 fixed in a upper main body frame 60 by drives72-1 and 72-2 such as linear motors. The support stands 71-1 and 71-2have thereon cameras 3-1 and 3-2 such as CCD (charge coupled device)frame accumulation mode cameras having automatic focusing function aswell as automatic aperture devices 3b-1 and 3b-2. Further, light sources2-1 and 2-2 such as parallel light sources with variable light quantityor stroboscopes are placed in a lower main body frame 61 opposedly tothe above cameras 3-1 and 3-2.

When measurement is performed on on-line basis in the formation meter50", the paper 1 on the line is fed between upper and lower main bodyframes 60 and 61 and images by transmitted lights from the light sources2-1 and 2--2 and coming through the paper 1 are caught by the cameras3-1 and 3-2. On the other hand, in the case where measurement isperformed on off-line basis, the paper 1 as sample is set between theupper and lower main body frames 60 and 61 and images by the transmittedlight from the light sources 2-1 and 2--2 and coming through the paper 1are caught by the cameras 3-1 and 3-2. The image from the light source2--2 caught by the camera 3-2 is in wide visual field while the imagefrom the light source 2-1 caught by the camera 3-1 is in narrow visualfield. Connected to the formation meter 50" shown in FIG. 17 are theimage processing computing element 5 and the fuzzy control unit 110similar to those in FIG. 3, though not shown in the figure.

FIGS. 18 to 24 show a procedure to control the formation by obtainingoptimal value of J/W ratio, using the formation meter 50" shown in FIG.17. Description is now given in detail on this procedure. Range of theJ/W ratio change is set to a predetermined range (e.g. 0.90 -1.10) andthe range of the change is equally divided (e.g. into 10 equal parts).For the paper 1 with J/W ratio being set to a predetermined value (e.g.0.90), images are caught by the lights from the light sources 2--2 and2-1 passing through the paper 1 by the cameras 3-2 and 3-1 in wide andnarrow visual fields, respectively. Based on each image, the formationfactors A and B are obtained by the image processing computing element 5from average primary variance a_(V) of density, secondary variance ofdensity V_(aV), variance V_(aaV) of the average value of density,frequency analysis specification in lateral direction and holespecification. By the same procedure, the formation factors A and B aresequentially obtained for the paper 1 in the case where the range of theJ/W ratio change is equally divided. As shown in FIGS. 18(a), 18(b),21(a) and 21(b), variation curves L_(A1), L_(A2), L_(B1) and L_(B2)showing the relationship between J/W ratio and the formation factors Aand B in wide and narrow visual fields are obtained. The formationfactors are not limited to A or B and variation curves may be obtainedfurther for formation factors C, D. . . .

Then, by the fuzzy control unit 110, in each of the above variationcurves L_(A1), L_(A2), L_(B1) and L_(B2), the area from lower to upperlimit of the formation factors A and B is for example equally dividedinto three parts in the direction of ordinate to `good area`, `fairarea` and `bad area`. Evaluation values for these good, fair and badareas are set to 1.0, 0.5 and 0.0 as shown in FIGS. 19(a), 19(b), 22(a)and 22(b) to obtain membership functions M_(A1), M_(A2), M_(B1) andM_(B2) showing the relationship between J/W ratio and evaluation valuesin wide and narrow visual fields.

Next, the membership functions M_(A1) and M_(A2) are overlapped toobtain wide-narrow visual field membership function M_(A12) as shown inFIG. 20 for the formation factor A through adoption of only a portionwhere the above two functions overlap each other. The membershipfunctions M_(B1) and M_(B2) are overlapped to obtain wide-narrow visualfield membership function M_(B12) as shown in FIG. 23 for the formationfactor B through adoption of only a portion where two functions overlapeach other. Further, the above wide-narrow visual field membershipfunctions M_(A12) and M_(B12) are overlapped with each other to obtainoverall membership function M as shown in FIG. 24 through adoption ofonly a portion where two functions overlap on each other. The center Gof gravity of the area surrounded by this overall membership function Mis obtained and is selected as optimal J/W ratio. J/W ratio iscontrolled to become the optimal J/W ratio. Alternatively, themembership functions M_(A1) and M_(B1) may be overlapped with eachother.

By the same procedure, center of gravity is obtained from overallmembership function for initial drainage by foils and the initialdrainage control is performed so that foil angle takes optimal value.Also, for finishing drainage by deflector, center of gravity is obtainedfrom overall membership function and the finishing drainage iscontrolled so that the deflector pushing degree and angle take optimalvalues.

Above all, in the case where there are two or more deflectors asdrainage elements in the finishing drainage, membership functions areobtained by changing combination of pushing degree with angle andoptimal values of pushing degree and angle are obtained for eachdeflector. Also, in the case where there are two or more foils in theinitial drainage, membership functions are obtained by changingcombination of angles of each foil and optimal value of angle isobtained for each foil.

Thus, membership functions are not prepared from the beginning in fuzzycontrol. But, control variables are respectively changed such as J/Wratio, foil angle in initial drainage, deflector pushing degree andangle in finishing drainage and evaluation values for each case arecombined to generate an overall membership function. As the result, morereliable control can be achieved and production of various types ofpaper can be properly controlled.

Further, because the cameras 3-2 and 3-1 are arranged for different wideand narrow visual fields as sensors and the sample information issimultaneously obtained, formations can be obtained both macroscopicallyand microscopically as numerical values and control closer to control byhuman vision can be accomplished. As described above, fuzzy control isperformed for J/W ratio, initial drainage and finishing drainage. Then,the range of the change around the optimal value of J/W ratio is setsmaller than the range of the J/W ratio change in the previous fuzzycontrol and J/W ratio is sequentially changed within the smaller rangeof the change. By the same procedure as above, center of gravity isobtained from overall membership function and J/W ratio control isperformed so that J/W ratio takes an optimal value obtained from thecenter of gravity this time. Initial and finishing drainages are alsocontrolled such that the foil angle and deflector pushing degree takeoptimal values obtained from center of gravity this time.

Thereafter, watching is effected and continued unless any troubleoccurs. When any trouble is detected such as decrease of formation dueto external change including raw material conditions, control isrestarted as described above (See FIG. 25).

In this way, range of the change of control variables such as J/W ratio,foil angle in the initial drainage and deflector pushing degree andangle in the finishing drainage, etc. are initially set to large valuesfor coarse control. After coarse control is completed, range of thechanges of each of the above control variables is set to smaller valuesand fine control is performed. Thus, in the initial stage ofpaper-making, products with considerable quality can be produced by thecoarse control with satisfactory yield and products of high quality withgood formation are obtained by the fine control.

Further, because the data obtained during fine control are accumulated,production of the same type of paper can be controlled later by onlyfine control. Reprocessing and rise-up times can be shortened and wasteof products during reprocessing and rise-up operations can beeliminated.

What is claimed is:
 1. A method for generating a paper qualitymembership function to be used in an apparatus for controlling thedegree of fiber variance in paper sheet, comprising the steps of:(a)picking up an image of transmitted light from a light source on an areaof paper by a plurality of cameras with different visual fields, thecameras being arranged so that images of the transmitted light arepicked up by the cameras concurrently in comparatively wide and narrowvisual fields and are introduced to a display unit of an imageprocessing computing element, there being means provided for changingthe visual field introduced to the display unit; (b) dividing the imageof the transmitted light on the display unit into a predetermined sizeand number of windows, the windows comprising pixels; (c) measuring thetone density of each pixel, and the tone density of each window from thetone density of the pixels comprising the window; (d) calculating valueschosen from at least one of the following:an average value of tonedensity and a primary variance of tone density of each window from thetone density of each pixel, an average value of the primary variance ofthe tone density for all of the windows, a secondary variance of tonedensity for all of the windows, and a variance of average values of tonedensity of each window; and (e) using one of or at least two incombination of said values as a formation factor; (f) changing thevisual field transmitted to said display unit by said plurality ofcameras; (g) repeating steps (a)-(e) one or more times to obtaindifferent formation factors; (h) generating a paper quality membershipfunction from the different formation factors obtained: and (i) usingsaid paper quality membership function to control the degree of fibervariance in said apparatus.
 2. The method according to claim 1, whereinthe light source comprises a stroboscope.
 3. A method for controllingthe degree of fiber variations in paper sheet, comprising the stepsof:(1) generating a plurality of paper quality membership functioncurves for categorizing the quality of the paper into categories rangingfrom lowest to highest quality, the categories corresponding toformation factors of the paper, the formation factors of the paper beingobtained by(a) picking up an image of transmitted light from a lightsource on an area of paper by a plurality of cameras with differentvisual fields, the cameras being arranged so that images of thetransmitted light are picked up by the cameras concurrently incomparatively wide and narrow visual fields and are introduced to adisplay unit of an image processing computing element, there beingprovided means for changing the visual field introduced to the displayunit; (b) dividing the image of the transmitted light on the displayunit into a predetermined size and number of windows, the windowscomprising pixels; (c) measuring the tone density of each pixel, andcalculating the tone density of each window from the tone density of thepixels of which the window is comprised; (d) calculating values chosenfrom at least one of the following:an average value of tone density anda primary variance of tone density of each window from the tone densityof each pixel, an average value of the primary variance of tone densityfor all of the windows, a secondary variance of tone density for all ofthe windows, and a variance of average values of tone density of eachwindow; and (e) using one of or at least two in combination of saidvalues as a formation factor; (f) changing the visual field transmittedto the display unit by said plurality of cameras and repeating the steps(a)-(e) so as to obtain a different formation factor corresponding tothe different camera position; (g) repeating step (f) one or more timesso as to obtain a number of formation factors from which a paper qualitymembership function curve can be calculated: (h) repeating steps (a)-(g)for a plurality of different paper sheets having highest to lowestquality so as to thereby obtain said plurality of paper qualitymembership function curves; (2) generating a plurality of separateoperation control membership function curves corresponding to operationfactors comprising, respectively, changes of J/W ratio, changes in foilangle, and changes in deflector pushing degree, said changes being inresponse to each of the paper quality membership function curvesgenerated in step (1), (3) obtaining a degree of matching atintersections of the paper quality membership function curves with eachof the operation control membership curves, (4) for the control of eachof said operation factors J/W ratio, foil angle, and deflector pushingdegree, in sequence,(A) obtaining in correspondence to each of thematching degrees, results of the estimated changes of the operationfactor from the respective operation control membership function curves,(B) overlapping and synthesizing results of the estimated change of theoperation factor to generate final operation control membershipfunctions providing a final estimated result of the change, (C)determining the actual change to be effected with regard to theoperation factor based on the final operation control membershipfunction, (D) adjusting the operation factor based on said determinedactual change, and (E) repeating steps (A)-(D) for each of the remainingoperation factors.
 4. The method according to claim 3 wherein theoperation control membership function is selected depending upon whetherany difference between the formation factor of a previous control andthe formation factor in a present control is positive or negative. 5.The method according to claim 3, wherein step (1) (f)comprisescommensurate with the starting of measurement, observing theformation of the entire paper by lifting at least one camera along arail to widen the visual field of the camera, gradually narrowing thevisual field of the camera by moving the camera down along the rail asthe formation is improved after starting the control by method, andlifting the camera up again to return to the initial large visual fieldfor monitoring when the formation is substantially stabilized.
 6. Themethod according to claim 5 wherein the range of change of controlvariables in J/W ratio, and in initial drainage and finishing drainageare initially set to large values for coarse control; and after thecoarse control is completed, the range of changes of each of the controlvariables is set to smaller values so that fine control is performed insteps.
 7. The method according to claim 3, wherein a plurality ofcameras for changeover are arranged to have different distances from thepaper; wherein step (1) (f) comprisesat the starting of measurement,observing the formation of the entire paper by one of the cameras withthe widest visual field; sequentially changing over to one of thecameras with a narrower visual field as the formation is improved afterstarting the control by said method; and changing over to the camerawith the widest visual field again for monitoring when the formation issubstantially stabilized.
 8. The method according to claim 7 whereinmonitoring is started in a status where the formation is beingstabilized in the control of the last stage.
 9. The method according toclaim 3, further comprising the step of frequency-analyzing the densityof image in the lateral direction to determine whether formation ispulling or pushing; and, in the case of pulling formation, the J/W ratiois increased and in the case of pushing formation, the J/W ratio isdecreased.
 10. The method of claim 3, wherein the foil angle isoptimized simultaneously for a plurality of foils for initial drainagecontrol, and wherein the deflector pushing degree is optimizedsimultaneously for a plurality of deflectors for finishing drainagecontrol.